An MRT train was 2/5 full of passengers. At the first station, 1/2 of the passengers alighted
and 17 people boarded the train. The train is now 1/4 full. How many passengers were there
on the train at first?

This time, I want to try so you can see how I think and from there I want to improve on my thinking
skills which I am lacking off.

Ok........First I take 1/2 minus from 2/5 = 1/5 (is this correct?)
Then.....I have to take the 1/4 = 1/5 + 17 (is this correct too?)

After that........actually I dont know already. Ha!
The only thing I can think of is that this is a "working backwards" problem sum.

Judy |------------------------------|------------------------------|------------------------------| 25|<----give away so we put it back
Jenny|--------------------|--------------------|-------------------| 1/4 |<----1/4 give away so we put it back

From here u can see 3/4 of Jenny equal to 2/3 of Judy, we have to refine the model, before that, we get the lowest common multiple of 2 and 3 which is 6

by obtaining the LCM of 4 and 5, which is 20, we are able to normalise/ convert the 1/5 and 1/4 into 4/20 and 5/20 respectively.
if memory serve me right, after obtaining the LCM, the students are to further divide the block into smaller size, subsequently they will be able to visual 1 block/unit of it is 17.

for non student, we get 1/4 - 1/5 = 1/20, from here we shall understand it is the 17 passengers that boarded the train.

For model involve fractions, students have to be able to get LCM, lowest common multiple, and resize the model into smaller units.